Jaco of course.. we all know that. but im going to say Colin Edwin of Porcupine Tree. Very unknown player but very much what I think a bass player should be in a band. he doesn't show off at all but manages to show his skills nonetheless.

I would say Jimmy Haslip. He is probably my favorite bass player right now. He can hold down a groove in just about any style like nobody's business. Partial resume: CSN, Bobby McFerrin, Bruce Hornsby, Lee Ritenour, Andy Summers, Marty Friedman (!). Also his soloing and fretless work is just some of the most stirring. Listen to the Yellowjackets' Four Corners, Politics, The Spin. Beautiful stuff. And last time I saw the Yellowjackets he was doing some just unbelievable soloing on a 6-string.

His knowledge is amazing...look at some of the articles he has written for 'Bass Player'.